Staphylococcus aureus: Difference between revisions

← Older edit

Content deleted Content added

VisualWikitext

Inline

Latest revision as of 16:17, 25 June 2025

Background

Microbiology

Facultative anaerobic, Gram-positive coccus
Catalase-positive and coagulase-positive
Microscopy: groups or clusters ("cluster of grapes")
Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar

Pathophysiology

Virulence Factors

Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL)
Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome
Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines
- Toxic shock syndrome toxin 1 (TSST-1) is implicated in Staphylococcal toxic shock syndrome
- Exotoxins B and C cause Staphylococcal toxic shock syndrome and also food poisoning

Antibiotic Resistance

Mechanisms of resistance are myriad
Common ones:
- bla gene encodes penicillinase, conferring resistance to penicillin
- mecA encodes PBP2a, conferring broad β-lactam resistance (MRSA)
- vanA on a plasmid confers vancomycin resistance (VRSA)

Clinical Manifestations

Colonization

About 20-30% of people carry it in their nares
See Staphylococcus aureus decolonization

Skin and Soft Tissue Infections

Boils and carbuncles
Cellulitis, usually purulent

Scalded-Skin Syndrome

Aka Ritter disease
Caused by exfoliative toxin A or B
Essentially bullous impetigo
Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)

Bacteremia

See Staphylococcus aureus bacteremia

Infective Endocarditis

Usually more acute presentation
High mortality
See Staphylococcus aureus endocarditis

Other Infectious Syndromes

Osteomyelitis
Native and prosthetic joint infection
Pyomyositis
Deep organ abscess
Surgical site infection
Pneumonia, especially ventilator-associated or influenza-related

Superantigen-Related Syndromes

Food poisoning
Staphylococcal toxic shock syndrome
- Classically tampon-associated
- Post-surgical (ENT): more of historic with changes in packing
- Surgical site infections, even without obvious signs of localized infection

Staphylococcus-Associated Glomerulonephritis

Occurs during acute infection
See also Staphylococcus-associated glomerulonephritis

Management

Choice of antibiotic depends on susceptibility testing, and duration depends on clinical syndrome

Penicillin-Susceptible Staphylococcus aureus (PSSA)

First-line: benzylpenicillin 2 million units IV every 4 hours, or 4 million units IV every 4 hours

Methicillin-Susceptible Staphylococcus aureus (MSSA)

First-line:
- Intavenous: cefazolin preferred to cloxacillin
- Oral: include cephalexin, cefadroxil, and oral cloxacillin
Others: clindamycin, fluoroquinolones, TMP-SMX, doxyxycline, erythromycin

Methicillin-Resistant Staphylococcus aureus (MRSA)

First-line: vancomycin
Others: linezolid (if lungs) and daptomycin (if blood), but also consider TMP-SMX, ciprofloxacin, doxycycline, and clindamycin

@@ Line 1: / Line 1: @@
-== Microbiology ==
+==Background==
+===Microbiology===
-* Facultative anaerobic, [[Has Gram-stain::Gram-positive]] coccus
+*Facultative anaerobic, [[Stain::Gram-positive]] [[Shape::coccus]]
-* Catalase and coagulase positive
+*Catalase-[[Catalase::positive]] and coagulase-[[Coagulase::positive]]
-* Microscopy: groups or clusters ("cluster of grapes")
+*Microscopy: groups or clusters ("cluster of grapes")
-* Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar
+*Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar
-== Pathophysiology ==
+===Pathophysiology===
+====Virulence Factors====
+*Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
-=== Virulence factors ===
+*Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL)
+*Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome
+*Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines
+**Toxic shock syndrome toxin 1 (TSST-1) is implicated in [[TSS|Staphylococcal toxic shock syndrome]]
+**Exotoxins B and C cause [[TSS|Staphylococcal toxic shock syndrome]] and also food poisoning
+====Antibiotic Resistance====
-* Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
-* Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL)
-* Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome
-* Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines
-** Toxic shock syndrome toxin 1 (TSST-1) is implicated in [[TSS|Staphylococcal toxic shock syndrome]]
-** Exotoxins B and C cause [[TSS|Staphylococcal toxic shock syndrome]] and also food poisoning
-=== Antibiotic resistance ===
+*Mechanisms of resistance are myriad
+*Common ones:
+**''bla'' gene encodes penicillinase, conferring resistance to penicillin
+**''mecA'' encodes PBP2a, conferring broad β-lactam resistance (MRSA)
+**''vanA'' on a plasmid confers [[vancomycin]] resistance (VRSA)
+==Clinical Manifestations==
-* Mechanisms of resistance are myriad
+===Colonization===
-* Two common ones:
-** ''bla'' gene encodes penicillinase, conferring resistance to penicillin
-** ''mecA'' encodes PBP2a, conferring broad beta-lactam resistance
+*About 20-30% of people carry it in their nares
-== Clinical Presentation ==
+*See [[Staphylococcus aureus decolonization]]
+===Skin and Soft Tissue Infections===
-=== Colonization ===
+*Boils and carbuncles
-* About 20-30% of people carry it in their nares
+*Cellulitis, usually purulent
-* See [[Staphylococcus aureus decolonization]]
-=== Skin and soft tissue infections ===
+===Scalded-Skin Syndrome===
+*Aka Ritter disease
-* Boils and carbuncles
+*Caused by exfoliative toxin A or B
+*Essentially bullous impetigo
+*Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)
-=== Scalded-skin syndrome ===
+===Bacteremia===
+*See [[Staphylococcus aureus bacteremia]]
-* Aka Ritter disease
-* Caused by exfoliative toxin A or B
-* Essentially bullous impetigo
-* Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)
-=== Bacteremia ===
+===Infective Endocarditis===
+*Usually more acute presentation
-* See [[Staphylococcus aureus bacteremia]]
+*High mortality
+*See [[Staphylococcus aureus endocarditis]]
+===Other Infectious Syndromes===
-=== Infective endocarditis ===
+*[[Osteomyelitis]]
-* Usually more acute presentation
+*[[Septic arthritis|Native]] and [[prosthetic joint infection]]
-* High mortality
+*[[Pyomyositis]]
-* See [[Staphylococcus aureus endocarditis]]
+*Deep organ [[abscess]]
+*[[Surgical site infection]]
+*[[Pneumonia]], especially ventilator-associated or influenza-related
+===Superantigen-Related Syndromes===
-=== Myriad other infections ===
+*[[Food poisoning]]
-* Osteomyelitis
+*[[Staphylococcal toxic shock syndrome]]
-* Native and prosthetic joint infections
+**Classically tampon-associated
-* Pyomyositis
+**Post-surgical (ENT): more of historic with changes in packing
-* Deep organ abscesses
-* Surgical site infections
+**Surgical site infections, even without obvious signs of localized infection
-* Pneumonia, especially ventilator-associated or influenza-related
+=== ''Staphylococcus''-Associated Glomerulonephritis ===
-=== Superantigen-related syndromes ===
+* Occurs ''during'' acute infection
-* Food poisoning
+* See also [[Staphylococcus-associated glomerulonephritis]]
-* [[Staphylococcal toxic shock syndrome]]
-** Tampon-associated
-** Post-surgical (ENT): more of historic with changes in packing
-** Surgical site infections, even without obvious signs of localized infection
-== Management ==
+==Management==
-* Duration depends on clinical syndrome
+*Choice of antibiotic depends on susceptibility testing, and duration depends on clinical syndrome
-=== Methicillin-susceptible ''Staphylococcus aureus'' (MSSA) ===
+=== Penicillin-Susceptible ''Staphylococcus aureus'' (PSSA) ===
-* First-line: [[cloxacillin]], then [[cefazolin]] or [[cephalexin]] (for oral)
+* First-line: benzylpenicillin 2 million units IV every 4 hours, or 4 million units IV every 4 hours
-* Others: [[clindamycin]], [[fluoroquinolones]], [[TMP-SMX]], [[doxyxycline]], [[erythromycin]]
-=== Methicillin-resistant ''Staphylococcus aureus'' (MRSA) ===
+===Methicillin-Susceptible ''Staphylococcus aureus'' (MSSA)===
-* First-line: [[vancomycin]]
+*First-line:
+**Intavenous: [[cefazolin]] preferred to [[cloxacillin]]
-* Others: [[linezolid]] (if lungs) and [[daptomycin]] (if blood), but also consider [[TMP-SMX]], [[ciprofloxacin]], [[doxycycline]], and [[clindamycin]]
+**Oral: include [[cephalexin]], [[cefadroxil]], and oral [[cloxacillin]]
+*Others: [[clindamycin]], [[fluoroquinolones]], [[TMP-SMX]], [[doxyxycline]], [[erythromycin]]
+===Methicillin-Resistant ''Staphylococcus aureus'' (MRSA)===
+*First-line: [[vancomycin]]
+*Others: [[linezolid]] (if lungs) and [[daptomycin]] (if blood), but also consider [[TMP-SMX]], [[ciprofloxacin]], [[doxycycline]], and [[clindamycin]]
 {{DISPLAYTITLE:''Staphylococcus aureus''}}